OK folks, strange situation. I have a commercial CO detector in the bus that has gone off many times. I assumed that it had a problem as my OLD battery operated detector showed no CO. The old battery unit is a Nighthawk and it seems to test just fine. I just looked at it and see that it was manufactured in Feb. of 1999!!!!

I got tired of carrying it back and forth between the bus and the house, so I got a new Kidde unit for the bus. On our last trip it went off when we were at the Eagle Rally with nothing running. I again assumed that it was defective.

When we got home, I got to playing with all three detectors in the bus. The commercial unit and the new Kidde unit both showed high levels of CO. The new Kidde read at least 180 PPM as I recall. The old Nighthawk showed zero. When I took the new Kidde outside it zeroed out. When I had it in the house it read zero. It appears to be working correctly. No obvious source.

When I put it back in the bus with the windows open (and bus in the shop), it eventually sounded an alarm (as did the commercial unit). Old Nighthawk showed zero. Again NOTHING was running that would generate CO as far as I can tell. Engine had not been run in 24 hours or more. No combustion generating devices that I can think of. Fridge is house 120V unit. After I turn on the roof vent, the count goes down.

So, ****WHERE IS THE CO COMING FROM*****??

Also, *******REPLACE ANY CO DETECTOR OVER 7 YEARS OLD (manufacturer recommendation)**********. I could have had a bad situation if I had relied on the old unit. Our house furnace is over 25 years old and I live in fear that it could go bad and flood the house. I relied on the OLD detector to protect us

I also think that both of the GOOD detectors are seeing something other than CO. The question is what. My super sniffer (Pat) is at a convention. However, when the detector went off at the rally, she did not smell anything, and we did not have any symptoms. The alarm was in the middle of the night and none of the neighbors had anything running. As I recall, we had the windows open, but the roof vent fan was not running.

Propane detectors pick up lots of gases (don't put the cat litter box in front of one ), but I don't know about CO and how they work.

Why not call Kidde tech support and ask them what else would trigger the alarm. You can't be the first one with an issue. I have found manufacturer's tech support to be a great resource for lots of things.

The 120-VAC units generally use MOS detectors, which are sensitive to a variety of gasses, including chlorine, bromine, and silicone vapors. An open bottle of bleach will set them off.

Battery-powered units generally use biomimetic sensors. These are sensitive to a narrower range of gasses. Their downside is that once they go off, they need to be left out in fresh air for a long time for the biomimetic disk to change color back to normal.

I would expect different readings from MOS vs. biomimetic detectors. That does not indicate a problem, just different operating modes.

I am guessing the two agreeing detectors are MOS and the disagreeing one is biomimetic. If so, check for sources of other gasses such as bleach, or formaldehyde (new carpet, etc.).

Didn't Craig Shephard or someone have an issue with battery outgassing causing the CO alarm to go off?

Yep, near as I can figure, by CO detector (RV unit) goes off when I charge batteries. Or maybe outgassing from by rigid insulation. Or maybe methane from the black tank as my vents were not workingright the last time I actually plugged it in and it went off.

I put a Nighthawk in to see if it was seeing anything, and it definitely was registering something, like you say. It went off in the middle of the night and my neighbor two doors down heard it.The batteries were on float. I finally decided the CO levels were corresponding with the charging of the batteries. Note that my batteries are in plastic boxes, but they are not vented outside. I've been looking for some way to add a power vent to the batteries that can't produce a spark. Maybe a bilge blower.

When the detectors went off, the batteries were on float. That would suggest they would not be generating much gas. I have them enclosed in a fabricated box that is vented outside the bus. I think it is pretty air tight.

I have not installed anything new in the bus in the last two years that would out-gas anything that would set off the alarm. Carpet is 4 years old as is most of the upholstery.

We do not get an alarm going down the road, so I don't think there is any engine exhaust issue. Having said that, we did have an exhaust pipe come loose in the engine compartment on the last trip. I am sure there was exhaust in the compartment, but it is pretty well sealed up and we did not get an alarm while driving or while parked shortly after we parked.

I need to point out the the 12V detector has gone off many times over the past few years. This is not a recent event. I had relegated to being a "defective" unit, but now I am pretty sure it is reporting correctly. The report event for this unit seems to be when parked for long periods with no obvious reason for the report (that is why I questioned the result)

We ran our generator quite a bit during our last two trips while parked, and did not get an alarm.

I have not run the Aquahot on diesel in quite some time.

I brought both of the battery units in the house yesterday and just took them back to the bus a few minutes ago. I closed up the bus. I will report the results later today.

I poked around with Google yesterday and did not see anything that would shed light on this situation. I did find some reports of older units giving false reports. In my case, the old unit does not give any report of CO, while the other two do report problems. I will probably buy another battery unit in the next few days and see what it reports.

Clifford, thanks for the reminder. We have a washer dryer in the bus and the "P" trap goes dry once in a while. I have plumbed in a small tube to the drain that I can run water to get the seal going. I will go run the water now to make sure the trap is wet.

When I talked about Pat's sensitive smell test, I obviously did not mean that she could detect CO. CO has no smell. What I was referring to was whether she could smell anything that might set the detectors off.

In the half hour since I took the units out this morning and closed up the bus, the CO level went to 77 as measured by the new battery unit. Both it and the 12V unit were sounding an alarm. The old unit reported zero (am sure it is dead).

I opened the window and ran the roof vent fan for a few minute and the level quickly dropped to zero and both functioning detectors showed a good condition.

I had re-plumbed the washer drain for another application that I no longer use. As a result, I was not "wetting" the P trap. I put the plumbing back to the original configuration and ran the water until I could hear it running into the gray tank.

We will see what happens later today.

I am very concerned that the old unit would "fail" in a non protective fashion. I would think the manufacturer should design the device to fail such that it reported a dangerous condition or give some other form of "fail" report.